Engineers initially had planned to pump in mud before the cement, but a BP spokesman said that wasn't necessary because there was no pressure building inside the well.

BP expects the well will be completely sealed — and declared permanently dead — sometime Saturday, five months after the catastrophe began April 20, when an explosion killed 11 workers, sank a drilling rig and led to the worst offshore oil spill in U.S. history.

The cement couldn't be pumped in until a relief well drill nearly 2.5 miles beneath the floor of the Gulf intersected the blown-out well, which happened Thursday.

The relief well was the 41st successful drilling attempt by John Wright, a contractor who led the team drilling the relief well aboard the Development Driller III vessel. Wright, who has never missed his target, told The Associated Press in August that he was looking forward to finishing the well and celebrating with a cigar and a quiet getaway with his wife.

"I am ready for that cigar now," Wright said in an e-mail Friday to the AP from aboard the DDIII.

The Gulf well spewed 206 million gallons of oil until the gusher was first stopped in mid-July with a temporary cap. Mud and cement were later pushed down through the top of the well, allowing the cap to be removed. But officials will not declare it dead until it is sealed from the bottom.

BP PLC is a majority owner of the well and was leasing the rig from owner Transocean Ltd.

The oil spill was an environmental and economic nightmare for people along the Gulf Coast that has spawned civil and criminal investigations. It cost gaffe-prone BP chief Tony Hayward his job and brought increased governmental scrutiny of the oil and gas industry, including a costly moratorium on deepwater offshore drilling that is still in place.

With oil still in the water — some of it still washing ashore — people continue to struggle. Fishermen are still fighting the perception their catch is tainted, and tourism also has taken a hit.